I have Cateye Mity 3 computer mounts on 4 bikes. I keep one Mity 3 on my Mtn bike with it's 26" wheels. I use the other Mity 3 and on any of my other 3 road bikes that all have 700-35 or 700-32 tires.
I park my daily commute bike in an enclosed steel bicycle locker just outside the entrance door of the building where I work. That bike locker gets hit by the sun pretty hard in the summer and the temperature cooks inside like an oven. I leave my sweaty bike gloves with my bike in the locker, and they are so dried out in the afternoon, you can stand them on end! Needless to say I've figured out that bike locker was causing my Cateye to get cooked too. I was puzzled as to why when I would leave work and start pedaling home, the Cateye would be dead. Finally my brain went into gear and I realized the Cateye and it's little watch battery was simply getting cooked. The computer would always work fine later in the ride and the next morning.